One of the most commonly used components in steel reinforcing for concrete construction, other than the bar, is a bar anchor. A common form of bar anchor is simply a bent or hooked bar end. The hook may be a 90.degree. or a 180.degree. bend. Typically, the hook forms the end of a bar. The hook may be embedded in a wall or column, while the rod projects into a beam or slab, or the hook is simply bent around the corner of a form. The rods may project through a form or into special bend-out boxes where pours are in sequence. More and more, protruding and bent bars are something to avoid for a variety of design, installation, and safety reasons.
Anchors are also widely used in dowel bar splices used in the formation of concrete pavement. The anchors may be straight or hooked sections of rod. The anchor may include a threaded socket which may be integral with or welded to the bar end. An example of the former is seen in U.S. Pat. No. 4,619,096, while an example of the latter is seen in the LENTON.RTM. FORM SAVER.TM. sold by Erico International Corporation of Solon, Ohio, USA. LENTON.RTM. is a registered trademark of Erico.
The threaded socket of the FORM SAVER.TM. includes a plate permitting the anchor to be attached to the inside of a form. After the concrete is cast and the form removed, the socket is available to enable a bar to be attached. If the threads are tapered, the attachment is with a few turns. Most such anchors include bent bar ends.
Bent or hooked bar ends or anchors have several drawbacks. They usually have to be sizeable to be effective. Also, the bending or rebending of the bar, especially a sharp bend, is often detrimental to the strength of the bar. If the anchor is to be placed in a relatively thin wall or column, the bend usually has to form a relatively sharp corner simply to fit. It is not uncommon for poor quality bar to snap, or certainly weaken when subject to such stress. Also, a small radius bend may not be permitted by design codes.
Another type of anchor is that simply using an oversize section of reinforcing bar. The oversize bar requires special treatment, and, unless bent, requires an inordinate length. An example of this type of anchor is seen in U.S. Pat. No. 5,131,204.
Another problem encountered with such anchors is bar congestion. Recent code changes have increased the amount of steel reinforcing required which results in bar congestion. These requirements, coupled with the desire of the owner or designer for more compact structural elements and less dead or unusable space, makes bar congestion a real problem for placement and installation of the bar. For example, it is not uncommon to have a shear wall only 200 mm thick. This greatly adds to the time and cost of installation, or building construction.
To alleviate some of these problems, there has been developed a headed anchor utilizing the principals of the Shear Cone Theory. The end of the bar is provided with a large heavy head. The inside of the head to which the bar is attached forms a theoretical shear cone resisting tension and having a wide transfer base in the concrete. This type of anchor is sold under the trademark LENTON.RTM. TERMINATOR.TM., also by Erico International Corporation of Solon, Ohio, USA. The headed anchor works on the same principal as a headed shear stud. The tip of the shear cone is, however, usually in one or two planes transaxially of the rod or stud. It would be desirable if the anchor would form the shear cones at varying axial locations with substantial area or deformations, and preferably continuously throughout its length, and still be overall of relatively short axial extent.
While the head on the end of the reinforcing bar makes an excellent bar end anchor, it cannot normally be used also as an anchor at a poured-in-place transition face, or at the face of a precast structure, since the hypothetical shear cone has little or no base. It would accordingly be desirable to have an anchor which may serve both as a bar end anchor and as a transition anchor at or near a form face. It would also be desirable to have such an anchor which does not require a hole in the form or a bar protruding through the form.